A conventional optoelectronic sensor uses a time-of-flight laser rangefinder system to measure the normal distance to a road surface from a fixed point above the road surface and then measure the distance to a vehicle which either passes or stops under the sensor. Because of the high repetition rate of the pulsed beam, traditional systems are able to develop a longitudinal profile of the vehicle using multiple consecutive range measurements as the vehicle moves under the sensor. Some conventional systems may also be able to determine vehicle speed and use this information to develop a profile of the vehicle.
Conventionally, the sensor receives a portion of the energy reflected from either the area or an object located within the area, such as a vehicle. The returned pulse energy is then provided as an input to a receiver for determining a time of flight change for pulses emitted and received, which may be caused by the presence of an object within the area. The sensor is also provided with various features useful in providing outputs which indicate the speed, census, size or shape of one or more objects in the area. For example, a typical sensor is provided with a component for receiving an input from the time of flight determining means and for providing an output indicating whether the object meets one of a plurality of classification criteria (e.g., is the object an automobile, truck or motorcycle).
Such sensors are being used as noninvasive solutions to track and analyze traffic across a wide range of applications, including toll collection, traffic flow analysis, bridge/tunnel clearance verification, as well as traffic control and surveillance. These applications have highly dynamic operating environments that demand very precise sensor tracking and detection capabilities. Conventional systems are still unable to accurately measure and track high speed traffic flow through a location with sufficiently high scan rates to enable vehicle identification and classification, particularly during inclement weather.
Accordingly, there is need for a sensor system with improved range accuracy and resolution at high scan rates. There is also a need for a sensor system that reduces false measurements arising due to adverse weather conditions.